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Discriminating Planetary Migration Mechanisms by Direct Imaging Norio Narita National Astronomical Observatory of Japan on behalf of SEEDS/HiCIAO/AO188 teams Clues to discriminate migration models small eccentricity and obliquity disk-planet interaction orbital eccentricity by radial velocity spin-orbit alignment angle by the RM effect large eccentricity or obliquity planet-planet scattering Kozai migration Can we discriminate two models? • Planet-Planet scattering Additional information from direct imaging! • Kozai migration We introduce a procedure to discriminate two planetary migration models by direct imaging. SEEDS Project SEEDS: Strategic Exploration of Exoplanets and Disks with Subaru First “Subaru Strategic Observations” PI: Motohide Tamura Using Subaru’s new instruments: HiCIAO & AO188 total 120 nights over 5 years (10 semesters) with Subaru Direct imaging and census of giant planets and brown dwarfs around solar-type stars in the outer regions (a few - 40 AU) Exploring proto-planetary disks and debris disks for origin of their diversity and evolution at the same radial regions Subaru’s new instrument: HiCIAO • HiCIAO: High Contrast Instrument for next generation Adaptive Optics • PI: Motohide Tamura (NAOJ) – Co-PI: Klaus Hodapp (UH), Ryuji Suzuki (TMT) • 188 elements curvature-sensing AO and will be upgraded to SCExAO (1024 elements) • Commissioned in 2009 • Specifications and Performance – 2048x2048 HgCdTe and ASIC readout – Observing modes: DI, PDI (polarimetric mode), SDI (spectral differential mode), & ADI; w/wo occulting masks (>0.1") – Field of View: 20"x20" (DI), 20"x10" (PDI), 5"x5" (SDI) – Contrast: 10^-5.5 at 1", 10^-4 at 0.15" (DI) – Filters: Y, J, H, K, CH4, [FeII], H2, ND – Lyot stop: continuous rotation for spider block Procedure to constrain migration mechanism Step 1: Is there a binary candidate? No! Kozai migration by a binary companion is excluded If a candidate exist → step 2 both p-p scattering and Kozai migration survive need a confirmation of true binary nature • common proper motion • common peculiar radial velocity • common distance (by spectral type) Procedure to constrain migration mechanism Step 2: calculate restricted region for Kozai migration The Kozai migration cannot occur if the timescale of orbital precession due to an additional body PG,c is shorter than that caused by a binary through Kozai mechanism PK,B (Innanen et al. 1997) If any additional body exists in the restricted region Kozai migraion excluded search for long-term RV trend is very important If no additional body is found in the region → step 3 both Kozai and p-p scattering still survive Procedure to constrain migration mechanism Step 3: calculate initial condition for Kozai migration Based on angular momentum conservation during Kozai migration, we can constrain the initial condition of the system : initial mutual inclination between the planetary orbit and the binary orbit can be constrained binary host star planet First Application: HAT-P-7 not eccentric, but misaligned (NN+ 2009, Winn et al. 2009) NN et al. (2009) Winn et al. (2009) very interesting target for direct imaging observation! Step 1: Direct Imaging Observations Subaru/HiCIAO Observation: 2009 August 6 Setup: H band, DI mode (FoV: 20’’ x 20’’) Total exposure time: 9.75 min Angular Differential Imaging (ADI: Marois+ 06) technique with Locally Optimized Combination of Images (LOCI: Lafreniere+ 07) Calar Alto / AstraLux Norte Observation: 2009 October 30 Setup: I’ and z’ bands, FoV: 12’’ x 12’’ Total exposure time: 30 sec Lucky Imaging technique (Daemgen+ 09) Result Images N NN et al. (2010) E Left: Subaru HiCIAO image, 12’’ x 12’’, Upper Right: HiCIAO LOCI image, 6’’ x 6’’ Lower Right: AstraLux image, 12’’ x 12’’ Constraints on other outer bodies H band contrast ratio 5σ detectable mass Contrast: [email protected]’’(100AU), [email protected]’’(160AU), [email protected]’’(320AU) Corresponding 5σ detectable mass: 110 MJ, 80 MJ, 70 MJ No further binary candidate was detected outer than 0.5’’ massive planets and brown dwarfs were not excluded at this point Characterization of binary candidates projected separation: ~1000 AU Based on stellar SED (Table 3) in Kraus and Hillenbrand (2007). Assuming that the candidates are main sequence stars at the same distance as HAT-P-7. Step 2: Restricted region for Kozai migration The timescale of Kozai migration in this system PK,B ～ ～ 300 Myr If a massive additional body with a shorter perturbation timescale exists, Kozai migration due to the binary cannot occur (Innanen et al. 1997, Wu and Murray 2003) conditional equation: (smaller bodies are allowed) Allowed region for additional bodies Kozai migration forbidden boundary Kozai migration allowed The Kozai migration cannot occur if the timescale of orbital precession due to an additional body PG,c is shorter than that caused by Kozai mechanism PK,B (Innanen et al. 1997) Possible additional planet ‘HAT-P-7c’ Winn et al. (2009c) 2007 and 2009 Keck data 2008 and 2010 Subaru data HJD - 2454000 Long-term RV trend ~20 m/s/yr is ongoing from 2007 to 2010 constraint on the mass and semi-major axis of ‘c’ (Winn et al. 2009) Initial position of ‘c’ In the presence of ‘c’ the Kozai migration due to a binary star could not occur in this system! Step 3: Initial configuration for Kozai migration If either of the candidates is a real binary, and no ‘c’ planet By the angular momentum conservation (Kozai mechanism) • • , : : semi-major axis and eccentricity of planet : mutual inclination between orbital planes of planet and binary • 0: initial condition, n: now necessary condition to initiate tidal evolution: within 82.5 – 97.5 deg (even for the most optimistic case) Summary for the HAT-P-7 case We detected two binary candidates, and calculated restricted region for a possible additional body Kozai migration was excluded in the presence of the additional body We can constrain migration mechanisms for other systems by this procedure Summary RM measurements have discovered numbers of ‘tilted’ planets tilted and/or eccentric planets are only explained by p-p scattering or Kozai migration RM measurements cannot distinguish between p-p scattering and Kozai migration from spin-orbit alignment angles Combination of direct imaging can resolve the problem there are numbers of interesting targets to pinpoint a planetary migration mechanism SEEDS can provide useful information for planetary migration